Hello @jtbrown Welcome to Connect. You should get several opinions because your case is not the usual ones that spine surgeons see. If you can take this to Mayo Clinic, I would recommend that because they will have surgeons who do a volume of unusual cases. Bending your neck and causing C4 and C5 to separate might be describing slipping of one vertebrae past the other. If that is significant, it may be able to contact the spinal cord.

A horizontal incision is standard for cervical fusion surgery and mine is like that and hidden in a crease in my neck. No one ever notices it. The spine can easily be accessed behind your trachea and esophagus and they retract it a bit to get behind it. That can cause trouble swallowing or even affect the function of vocal cords which are risks to a frontal surgical path. I had throat pain with swallowing for about 3 weeks.

My surgery was at Mayo. I had spinal cord compression from a ruptured disc that was growing bone spurs in the central spinal canal. A question to ask would be about what to do about the fused C3/C4 and what will likely happen there in the future if nothing is done. That doesn't just happen to a healthy spine. Bone remodels and will grow spurs from pressure on the end plates (that abut the discs). Do you have good bone quality or is there possibly of some compression happening like that which happens with osteoporosis and compression fractures? Have you had an injury that led to this current condition? Will it continue to fuse and entrap nerves or the spinal cord? That is something a lot of surgeons won't want to touch because it fused itself and because levels at C3 are risky to work on because of the nerves for life support of your heart and lungs exiting the spinal cord near there. Bone quality or lack of it can affect the success of spine surgical outcomes. This is why Mayo or another medical center of excellence would be a good choice. Mayo is known for taking more difficult cases that others refuse which may give you a better chance of getting in if you have insurance that Mayo accepts.

It does sound like you are headed for some spinal fusion which will change your ability to bend your neck and turn your head. There may be different ways that surgeons will solve this, so that is why several opinions would be helpful before you go forward with surgery. I would highly recommend my neurosurgeon at Mayo, Jeremy Fogelson. He can review your case if you apply for care at Mayo if you request him. He does both fusion and artificial disc surgeries and teaches lab courses for other surgeons in these techniques. Here is his profile.
https://www.mayoclinic.org/biographies/fogelson-jeremy-l-m-d/bio-20055624